This invention relates to a method and apparatus for the continuous production of reinforced profile belts from extrudable material provided with a stretch resistant insert. The extruded material stream passes between the two circulating halves of a divided former. The former halves are endless loops which converge along a portion of their lengths to form a closed former segment.
It is essential with profile belts, particularly toothed belts subjected to high performance demands, that an inner seal be formed between the material comprising the body of the belt and a strengthening insert strip. The tractive force is thereby transferred from the teeth to the insert strip without causing the strip to shift inside the belt. It is also important that the reinforcement or insert strip be firmly secured in the neutral zone of the belt and that the insert be completely surrounded by the synthetic material comprising the body of the belt.
Known methods of producing profile belts have not always met these desired criteria. German OS 21 23 902 teaches a method for the continuous production of reinforced profile belts from extruded material with a stretch resistant insert strip. The two endless circulating halves of a divided former converge along a portion of their lengths. The nozzle of an extruder forms a seal where it fits between, and opens into the closed former halves. The length and rotational speed of the closed former and the extrusion rate of the extruder are calculated so that the former cavities at the end of the closed former segment are sealed by the solidified material. A back pressure is produced which compensates the volume for shrinkage until the material hardens. The fact that the closed former segment with the cavities is formed by an endless belt wrapped around a turning wheel, thus giving it a circular arch shape, and the manner in which the synthetic material is injected into the former cavities and the stretch resistant insert strip is introduced, prevent this method from completely satisfying the criteria set out above. In particular, it is impossible to completely surround the insert strip with synthetic material. This is evident in FIG. 6 and from the second paragraph on page 10 to the first paragraph on page 11 of the specification of German OS 21 23 902, since the drivers 19 leave blank places on the reinforcement or insert strip 17.
In the embodiment according to FIG. 3 of this German OS (also see page 10 there, the last three lines) it appears that synthetic material 21 is placed on the comb surfaces 14 through the auxiliary nozzles. There the material hardens by appropriate temperature treatment of the former wheel (compare page 11 of the mentioned German OS, fourth line). However, in practice unexpected difficulties arise. Thus, it is unavoidable that the hot reinforcement 17 pushes its way through the newly hardened, thin layer of plastic and directly touches the comb surfaces 14 of the teeth, which results in undesirable blank places. Further, the insert strip no longer lies in the neutral zone.